1. Field of the Invention
The present invention relates to a display apparatus including organic light-emitting devices.
2. Description of the Related Art
In recent years, much attention has been focused on display apparatuses including self-luminous organic electroluminescent devices in view of power saving and thickness reduction. A display apparatus includes a plurality of organic light-emitting devices which are arranged in a display region and which each include a pair of electrodes and an organic light-emitting layer sandwiched therebetween.
The organic light-emitting devices are extremely sensitive to moisture and oxygen. The presence of moisture in the organic light-emitting devices causes deteriorations; hence, non-luminous region called dark spots are caused in the organic light-emitting devices and/or the light emission efficiency of the organic light-emitting devices is reduced. Since such deteriorations cause a reduction in display function, the following configuration is used: a sealing configuration in which a sealing substrate with high moisture barrier properties is bonded to a substrate to cover the display region such that moisture and oxygen are prevented from penetrating the organic light-emitting devices.
For the purpose of increasing the percentage of a light extraction area, top emission-type organic luminescent display apparatuses are under development. A top emission-type organic luminescent display apparatus includes driving circuits including thin-film transistors (TFTs) and the like and organic light-emitting devices arranged above the driving circuits. Layers included in the organic light-emitting devices are extremely thin and therefore are readily broken by irregularities due to the driving circuits. Therefore, the irregularities due to the driving circuits are usually planarized in such a manner that the driving circuits are covered with a planarization layer made an organic material.
The planarization layer has a function of protecting the driving circuit from damage during processing. In order to omit an unnecessary space in a surface of a substrate, the driving circuits are arranged over the substrate and the planarization layer usually extends over the substrate.
When the planarization layer continuously extends over the substrate, the planarization layer has an exposed portion extending out of an sealing substrate and moisture and the like penetrate the exposed portion. The moisture and the like penetrating the planarization layer reach the organic light-emitting devices to cause the deterioration of the organic light-emitting devices. Japanese Patent Laid-Open No. 2004-335267 discloses a technique in which a separating region is provided around a display region by partly removing a planarization layer and a sealing substrate is bonded to a portion of a substrate that is located outside the separating region as shown in FIG. 5. The separating region is disposed in the planarization layer and blocks a moisture pathway extending in the planarization layer; hence, organic light-emitting devices can be prevented from being deteriorated by moisture and/or the like.
Japanese Patent Laid-Open No. 2003-282240 discloses another technique for protecting organic light-emitting devices from moisture, that is, a sealing configuration in which a display region is covered with an organic protective layer made of an organic material and the organic protective layer, a peripheral portion thereof, and a surrounding portion thereof are covered with an inorganic protective layer. After irregularities caused by inclusions adhering to a surface of the display region during processing are planarized with the organic protective layer, the organic protective layer is covered with the inorganic protective layer, which has high moisture barrier properties. Therefore, defects caused in the inorganic protective layer by surface irregularities can be reduced, resulting in increases in moisture barrier properties of the inorganic protective layer.
In view of thickness reduction, weight reduction, cost reduction, a sealing technique using a protective layer including an organic protective sub-layer and an inorganic protective sub-layer deposited thereon is more preferable than a sealing technique using a sealing substrate. In the case of sealing a display apparatus including a planarization layer continuously extending over a substrate, the direct application of the technique disclosed in Japanese Patent Laid-Open No. 2003-282240 is not effective in obtaining sufficient sealing properties. This is because although the display region is covered with the organic protective layer and the organic protective layer, a peripheral portion thereof, and a surrounding portion thereof are covered with the inorganic protective layer, moisture and the like penetrate the display region through the planarization layer.
In the technique disclosed in Japanese Patent Laid-Open No. 2004-335267, the substrate, which has the planarization layer having the separating region, is sealed. If the organic protective layer extends across the separating region, moisture and the like penetrate the display region through the planarization layer and the organic protective layer. An etchant penetrates an end portion of the planarization layer that is in contact with the separating region and therefore the planarization layer is likely to be stripped off. This causes a problem that a driving circuit cannot be sufficiently protected and the display performance of a display apparatus cannot be secured.